The present invention relates to a self-controlling drill rod for rotary boring tools of machine rock tools.
The inventive self-controlling drill rod is disposed behind the boring tool and generally in the vicinity thereof. Its inner drilling shaft is directly connected so as to rotate in particular with the deepest drill rod and with the boring tool. The boring tool used is, for example, a boring head equipped with a plurality of cross roller bits. The self-control therefore works directly behind the free cut of the boring tool, so that each deviation of the boring tool from the predetermined direction of boring is corrected so quickly that the direction of boring virtually coincides with the desired direction. The self-control means required therefor is placed with its various systems in the vertical housing which encloses the drilling shaft. On the outside the housing bears the control bars offset by equal angles of arc and pivoted at one end, which cooperate with the borehole face to apply the necessary correction forces. The housing contains chambers which accommodate the sensors designed as gradometers, the system serving to drive the control bars, which can swing out the control bars individually in accordance with the particular deviations, and the control electronics and possibly special electronics for acting on a measurement/pressure pulse generator which transmits data on the drilling progress via the borehole fluid. The housing also contains the stator of a generator that generates the electrical energy for the electronics and electrical system.
The chambers are generally placed one behind the other in radial projections of the vertical outer body which are placed behind control bars mounted at the end of the housing facing the rods and connected to the path limiter at the end facing the boring tool. This results in a space saving arrangement which allows for rods for borings with relatively small diameters, e.g. of 21.6 cm.
The rotary boring rods with which the inventive self-controlling drill rod is used are generally driven by a drill motor set up outside the boring. Such machine rock drills operating by the rotary drilling method produce borings sunk from the top to the bottom, in which the borehole fluid serves to carry the debris removed from the bottom of the borehole by the boring tool toward the top and out of the boring. This flushing can be performed with water with the inventive apparatus as well if the lifting speed is sufficient in the borehole, but weighted fluids producing an additional lift, which are known in the form of gel or mud having thixotrope properties when weighted, e.g. by bentonite, are also suitable. Since gravity supports the removal of debris from the borehole when drilling from the bottom to the top, the inventive apparatus can also be used for such borings provided drilling fluids are provided, for instance, to cool the bits.
The borehole mud flowing in the area between the boring rods and the borehole face can be used to transmit measured values. Part of the electrical system is then used for the hydraulic control of the pressure pulse generator which is mounted in the shaft and changes the cross-section of the flush channel. However, the hydraulic control of the pulse generator must be provided in the outer body.
Due to the largely miniaturized hydraulics in view of the lack of space in the housing, such self-controlling drill rods make it necessary to place high demands on the cleanness of the hydraulic working fluid and also to protect the mechanical parts, e.g. the bearings of the drilling shaft, which are especially sensitive to the penetration of debris.
The invention assumes a known self-controlling drill rod of the type described at the outset (Gluckauf journal 120 (1984) no. 13, pp. 819,822). One of the above-mentioned chambers serves here as a tank for the hydraulic working fluid (consisting of oil) of the hydraulic pumps for the pistons provided behind each control bar in the rods. The pumps constitute the pressure generators of the system and are driven mechanically, e.g. via an eccentric of the drilling shaft. The hydraulic control of the pressure pulse generator necessitates a number of rotary transmission leadthroughs of the drilling shaft in the housing, which are provided with soft seals sealed on the drilling shaft for sealing the working fluid of the hydraulic system pressurized at, e.g., 100 bar. The radial bearings of the drilling shaft are seated in the end of the housing, which are supplemented by an axial bearing disposed behind the radial bearing in the housing on the side facing the boring tool. These drilling shaft bearings are designed as rolling bearings to obtain an easy-running shaft in the housing. The faces of the housing are provided with rotary seals to protect the drilling shaft bearings, separating the bearing lubrication from the borehole mud and relieving the soft seals.
On the one hand, the described construction of these seals is elaborate and susceptible to disturbance due to the great number of their components. On the other hand, the sealing pressure of the rotary seals does not suffice for high pressures of the borehole fluid, as are encountered in the case of deep borings which must be sunk over several hundred or even thousand meters. The rotary bearing rings sealing against one another must be isolated. But even at small depths a lubricant wedge still forms between these rotary seal surfaces rubbing against each other. Even if they are mounted with the greatest care, the drilling shaft and the housing perform radial motions which also act between the rotary seal surfaces sealing against each other and provided with lubricant. This causes extremely fine debris to be drawn out of the borehole fluid into the above-mentioned lubricant wedge. These particles have an abrasive effect on the polished rotary seal surfaces rubbing against each other. This ultimately causes parts of the debris to come between the drilling shaft and the housing. They soon destroy the shaft bearings and also attack the generator, hydraulic pumps and soft seals of the rotary transmission leadthroughs. The damage or destruction of these parts is particularly dangerous because it may cause the oil serving as the working fluid to be lost. The entire amount of oil present is very small, so that even small losses of oil may cause the entire system to break down. Furthermore, contamination of the oil leads to considerable disturbances in the following hydraulic components of the system.
When such disturbances occur, they take place at varying depths in increasingly short time periods. They can only be eliminated when the apparatus is dismantled. This requires the entire boring rod system to be moved out of the borehole. The time period lost thereby and by moving the rods back in are unacceptable when they are more frequent than the time periods required for changing worn out boring tools.
The invention is based on the problem of simplifying the structure of the self-control means for a self-controlling drill rod having the features explained at the outset, and ensuring that the service life of the parts important to the system is at least great enough, independently of the pressure of the borehole fluid and thus of the depth of driven borings, to equal the service life of the boring tools.
According to the invention, the hydraulic differential pressure prevailing between the boring rod fluid in the flush channel of the drilling shaft and the borehole fluid at the particular end of the housing is utilized to prevent contaminated drilling fluid from passing out of the borehole into the housing, by branching off a partial current of the in-flowing fluid largely free from debris as the working medium of the hydraulic system. This differential pressure produces a pressure gradient from the annular space into the borehole, so that no debris can flow back. On the other hand, this pressure gradient is relatively small so that small pressure differences also prevail before and behind the check valves separating the clean borehole fluid from the contaminated borehole fluid, which considerably simplifies the structure of such valves.
The invention also utilizes the relatively clean boring rod fluid as the working fluid for the hydraulic system of the self-control means, which performs necessary work, for instance, in the drives of the control bars. This allows for the self-control means to be realized with a simplified hydraulic system even for very deep borings with accordingly high hydraulic pressures. The above-described rotary transmission leadthroughs are under the high hydraulic pressure of the fluid on the outside, and under the system pressure on the inside, resulting in small differential pressures in deep borings so that the soft seals can also be used here.
It has been shown that, in spite of the sensitive components of the hydraulic system of the self-control means, not only fluids consisting of water or gels are suitable as working fluids but also thixotrope muds, if they are separated from the borehole fluid and are therefore essentially free from debris. All types of fluids do acquire parts of the debris in the course of their use in the flushing cycle. But since the invention involves branching off a partial current of the fresh fluid, i.e., the boring rod fluid, into the annular space, dangerous contamination of the hydraulic working fluid can be counteracted. After the boring rods have been raised, the borehole fluid still stands in the borehole, but the fluid filling of the annular space can be maintained when the boring rods are being moved in and out by built-in check valves, thereby preventing debris from penetrating.
This also makes it possible to include the bearings in the boring rod fluid of the annular space and cool them with this fluid. The check valves have mainly a dirt-repellant effect on the debris of the borehole mud.
A further advance may be achieved by using the clean boring rod fluid to drive a pulse generator by generating the necessary pressure with a pump mechanically derived from the boring rods. This makes it possible to shape the pulses rendering the measured values in such a way they can be read off a differential pressure sensor at the borehole mouth without error.
The above-mentioned possibility of using boring rod fluids contaminated with particles of debris without any trouble in the inventive way as described above may be realized by providing a radial bore extending as far as the flush channel and having a filter built in which is acted on by the fluid from the flush channel, because suitable filters or filter media are available and have sufficient service lives, so that the regular removal of contaminated filters after the rods are raised to change the boring tool suffices to eliminate this source of trouble.
The check valves required at the ends of the housing or the annular space can be of relatively simple design. The valve body is formed by a metal ring placed in a groove in the vertical housing and biased with an annular spring assembly, for example, toward the valve seat which is placed in axially immovable fashion in a groove in the drilling shaft or a drilling shaft flange. Such metal rings are a known kind of seal and are suitable for rough operating conditions, like those occurring, for example, in construction engineering. They are particularly expedient as check valves for the purposes of the invention because their spring power is strengthened by the pressure of the borehole fluid applied on the outside and because the pressure gradient directed from the inside toward the outside prevents abrasive particles of the debris from coming between the metal ring surfaces projecting onto each other.